I have a 400ft well, and I want to have a buzzer comes on every time water drops below certain level(280ft). At the moment, I got it working using a 12V battery and a multi-meter. I dropped down an electrical wire(2 wires). Now the top ends are connected as follow: One to Battery Negative and the other to Multi-meter negative. Multi-meter positive is connected to Battery Positive. This works fine, and the multi-meter reads 12V whenever the wire is submerged in the water. No reading when it's not.
Like I said at the beginning, I would like to have a buzzer, so I tried it using a transistor, a buzzer and couple resistors. Since water is not a good conductor, it did not work. The only way it worked is by adding a cork. The cork is hollow, and I inserted a metal plate, so water lifts or drops the cork for contact. I also tried a five pin normally open/ normally closed relay. Same result, not enough amperage to trigger the relay. Had to use the cork again. The cork won't fit thru the well. Testing was done outside the well.
Now the Pros of this method: I feel like I could do it.
Cons: Am I creating some electrolysis that eventually corrode the copper wires?
Anything other suggestions or different ways? What about using arduino ? Could it act as a voltage sensor like a multi-meter then triggers a relay or something? Any ideas will be appreciated.